IBM has just today released a presentation that explains CMM1 and CMMA in a bit
more
detail, and shows some performance gains achieved by using them. They also give
the
required levels of Linux, hardware and z/VM needed, plus any necessary APARs.
The
presentation can be found here:
http://www2.marist.edu/~mvmua/08101530.ppt
Enjoy....
David Kreuter wrote:
Would IBM care to comment to this group concerning CMMA? I am about to embark
on a
benchmark of CMM and CMMA. During my initial playing with setup of CMM and
CMMA, I
have found CMMA to be much easier. Being lazy I like the Ronco oven approach (
sorry if
you don't watch infomercials) of "set it and forget it". I too want performance
data so
don't misinterpret the previous sentence.
I like the idea of linux checking/setting extended hardware bits and then DIAG
10
RELPAGing. CMMA is just CMS on steroids. With the ballooning approach of CMM
there is
more work to do, plus I wouldn't rush into using production servers on the
shared
memory pool. I want favored nation status for production servers.
Something appeals to me about the intrinsic nature of having the kernel decide
which
page to DIAG 10 when CMMA is used. I realize that there are implications of
doing this
for System z far beyond our mainframe shores but frankly I don't care. We
need all
the help we can get managing our expensive memory plus we have to deal with our
naughty
WAS children that never drop from queue. I'm expecting big things from CMM
and/or
CMMA.
David Kreuter
________________________________
From: Linux on 390 Port on behalf of Rob van der Heij Sent: Wed 12/17/2008
11:16 AM To:
[email protected] Subject: Re: Over Committing Storage in z/VM
2008/12/17 ???? ???? <[email protected]>:
Anyone here using CMM for over committing? It sounds great! is it working great
as
well?
It's so great there are even two of them ;-)
CMM-1 (also called ballooning) is to temporarily take away memory from Linux
when it
should not be using it. Can be used if you understand the application
requirements in
Linux, for example with a TSM backup that should have memory over night but not
during
daytime. Or when you have an external process that can take VM performance data
and
decide how much Linux can have or needs.
CMM-2 (or CMMA - requires adequate hardware and software) This is supposed to
happen
all automatic with no tuning options and no instrumentation on what it does...
Current
software levels don't enable it per default, and future levels may not include
the full
feature anymore. For CMMA, I used to say "It is a very cool research item. In
lab
environment, an artificial workload could be constructed that takes advantage of
it."
Any performance data I have seen from IBM confirms this status.
And for completeness, there is CMM-0 ;-) Make sure your virtual machines drop
from
queue when idle, so z/VM can do memory management. Tune the ratio between
high-performance swap and virtual machine memory based on the workload
characteristics
and business justification (so a test server has higher latency and lower
cost). Look
for my post on Nov 27th:
www.mail-archive.com/[email protected]/msg50668.html
(Google found it searching for ""real disks for swap is only good for slowing
down
Linux")
Rob
Rob van der Heij Velocity Software http://www.velocitysoftware.com/
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V/Soft
z/VM and mainframe Linux expertise, training,
consulting, and software development
www.vsoft-software.com
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